Do you think there is one simple answer?
For one, there are issues with error in the opinion polls you are quoting. As discussed before, there are a lot of reasons for those errors. Other reasons may include, opposition to obamacare, fear of government controlling heath care, not wanting to pay for other people's healthcare, strong affinity for the conservative candidate overall, strong dislike for the progressive candidate overall, right wing propaganda via FOX and talk radio and fear of change.
I point to the fact that opinion polls and voter history in many districts aren't coherent on this issue and say it's clear that opinion polls don't predict voting behavior. When a statistical tool turns out to be unreliable, it's best to not use it until it has been shown to be reliable.
Well, this is your opinion. I'm not motivated to discuss it because you have no facts to back it up. In fact, your opinion is based upon a false assumption. It is false to say Democrats aren't running candidates who support universal healthcare in 2018 primaries in conservative districts.
I'd like to think your opinion to be true and I'd like to think that Universal healthcare will turn support for Democrats. In my opinion, people who vote for right wing candidates are more conservative than the opinion polls which are riddled with errors would say. That said, I am interested in following how Justice Democrats progress through the 2018 election cycle.
From what I've read of the West Virginia primary the Justice Democrats candidate isn't doing very well.